The present invention relates to a process for preparing substituted benzoyl chlorides by chlorinating the corresponding benzaldehydes. Substituted benzoyl chlorides may be considered activated derivatives of the corresponding benzoic acids. For this reason they are widely used as valuable synthesis building blocks, for example as intermediates for producing plant protection agents and drugs and for producing dyes and plastics.
Aromatic carboxylic acid chlorides are customarily prepared by reacting carboxylic acids with a chlorinating agent or by partial hydrolysis of benzotrichlorides. An important advantage of these processes is based on the fact that the corresponding starting materials are available on an industrial scale, because they are easily accessible. These favorable preconditions are not present in the case of preparation of substituted benzoyl chlorides, since the corresponding starting materials, i.e. appropriately substituted carboxylic acids or benzotrichlorides are generally not readily accessible and also are not usually available in industrial quantities.
It is known that starting from aldehydes, by halogenating the aldehyde group, carboxylic acid halides are accessible directly.